The present invention relates to a device for determining the characteristics of particles in suspension in a liquid. The invention more particularly applies to determine the characteristics of paper paste constituents during paper manufacturing. It especially permits measurement of parameters such as length, width, curvature and ratio between organic elements and mineral elements.
Suspensions such as paper pastes comprise fibrous organic elements and mineral elements having very diversified shapes, sizes and ratios that have to be known because the properties of the finished product largely depend upon those parameters. Particles comprise fibers, the largest size of which ranges from a few tenths of a millimeter to over one centimeter, which are in suspension in a liquid, usually water.
In the prior art, numerous processes for determining the characteristics of particles in suspension, such as fibers and mineral fillers contained in a paper paste, are known.
Apparatuses have been proposed wherein particles in suspension in a liquid are forced to pass through a transparent cell which is lighted, for example, by a coherent light source, allowing the various following steps to be carried out:
measuring the fiber length by forming the fiber pattern on photodetector lines and counting the number of exposed photodetectors, PA1 measuring a size corresponding to their diameter by analyzing the diffraction and diffusion patterns, and PA1 measuring the ratio between cellulose fibers and mineral fillers by measuring the depolarization of a light source direct flow.
In case of length measurement, the drawback of this type of apparatus is that it requires the use of an optical measurement cell formed by a small-diameter capillary tube so as to strictly limit the number of fibers that flows therethrough at a given time in order to be able to form individual fiber patterns and to measure the length of the fibers. Indeed, if a large number of fibers simultaneously arrives, their patterns cannot be separated and length cannot be measured. The drawback inherent in the use of a small-diameter capillary tube is that, in addition to an increase in measurement time, in practice such a capillary tube is liable to be clogged by accumulation of particles or by a larger particle. As a result, the above processes using optic measurement cells are not used for industrial manufacturing purposes but only in laboratories by sampling and individually examining those samples.
Independently of the apparatuses for measuring morphologic parameters of fibers or other elements in suspension in a liquid, particle fractionation apparatuses have been used in the paper industry, for sorting paper paste constituents as a function of the fiber length. An exemplary apparatus is described in an article by Gunnar OLGARD issued in TAPPI, Vol. 53, No. 7, July 1970, pages 1240-1270.
Such a fractionation apparatus, or fractionator, comprises a tube through which flows a liquid (eluant) between two air bubbles and in which the particles already in suspension are injected. Particles are then concentrated in suspension and sorted. In paper industry, eluant is generally water. By sending the output product of such a hydrodynamic fractionator into different vessels, for example positioned on a turntable, each of the vessels is filled with eluant containing fibers according to a given range of lengths.
A fractionator is not a measurement apparatus but a sorting device.
An object of the invention is to provide for an apparatus measuring the quantity of particles fractionated by range of size as well as characteristic parameters of fibers or other components in suspension in a liquid, this apparatus having the advantage of being usable for industrial purpose and to permit a periodical follow-up, substantially in real time, of a paper paste in suspension flowing in treatment tubes.